This study presents the antifibrotic effect of interferon gamma (IFN-gamma) in silicosis of rats. Wistar rats were received saline or 20 mg of quartz by intratracheal instillation. The next day after instillation, silicosis model of rats were daily treated IFN-gamma (1.0 x 10(5) units/rat) or saline by intramuscular route. At 1 month or 2 months after instillation, rats were sacrificed to determine hydroxyproline content and observe the change of fibrosis and expression of interleukin-4 (IL-4) and transforming growth factor-beta1 (TGF-beta1) in the lung of rats. The hydroxyproline content of IFN-gamma treated groups was significantly lower than that of quartz groups (P<0.05). At 1 month after instillation, there were Stage II and II+ of silicotic nodules in quartz group; however, in IFN-gamma treated group only cellular nodules (Stage I) were observed. At 2 months after instillation, there was Stage II+ and III of silicotic nodules in quartz group. In IFN-gamma treated group Stage II was found. The expressions of IL-4 (2.19+/-0.90, 0.61+/-0.22, respectively) and TGF-beta1 (1.37+/-0.31, 1.76+/-0.72, respectively) in IFN-gamma treated groups were significantly lower than those in quartz groups (IL-4: 3.33+/-1.27, 1.99+/-0.80; TGF-beta1: 3.67+/-0.63, 4.90+/-1.11, respectively; P<0.05 or P<0.01). It may be concluded that the decreased expression of IL-4 and TGF-beta1 may be associated with decreased hydroxyproline synthesis, which then results in decreased lung fibrosis.